1. Field of the Invention
The present invention relates generally to hydraulic brake boosters for use with an open or circulating fluid pressure system, and more particularly to a hydraulic brake booster mechanism which facilitates an emergency application of the brakes upon the failure of the pressure source.
2. Description of the Prior Art
Conventionally, the various brake booster mechanisms, with emergency brake application means, which have been proposed include a first valve means for controlling or delivering the fluid pressure from a pump to a power piston for the brakes, and a second valve means for delivering the emergency fluid pressure to the power piston for the brakes upon the failure of the fluid source or pump.
The second valve means, however, is arranged and designed to be opened or operated by means of an excessive movement of the first valve means, and consequently, there is a disadvantage in that the second valve means is forced to be opened due to a sudden brake application being required or an excessive force acting upon the brake booster depending upon the excessive depression force of the brake pedal or the like even when the pump normally operates. The emergency fluid pressure within the accumulator is then used for the brakes even during the normal condition of the fluid source, and thus, the emergency fluid pressure or supply of the accumulator may be depleted. This results in a lack of emergency pressure for the brakes when the emergency fluid pressure is in fact required.